Ferrous chloride is produced by reaction of the synthesis hydrochloric acid and ferrous oxide, while ferric chloride is produced by the chlorination of ferrous chloride. Both products are available in the technical or drinking water treatment grade. The drinking water treatment grade is divided, depending on the application, in standard or extreme grade. Ferric chloride, at 40%, is widely used in the purification of drinking water, in the treatment of wastewater or industrial water. Ferrous chloride, at 30%, performs, among others, a function of control and abatement of hydrogen sulphide, the reduction of phosphorus, chromates and the elimination of cyanides in the water to be purified.